1. Field of the Invention
This invention relates in general to circuits and methods of operating electronic devices, and more particularly, to circuits including parallel conduction paths and methods of operating electronic devices including parallel conduction paths.
2. Description of the Related Art
Organic electronic devices have attracted considerable attention since the early 1990's. Examples of organic electronic devices include Organic Light-Emitting Diodes (“OLEDs”), which include Polymer Light-Emitting Diodes (“PLEDs”) and Small Molecule Organic Light-Emitting Diodes (“SMOLEDs”). Display devices, including OLED displays, have played an important role in modern human life. As computing, telecommunications, home entertainment, and networking technologies converge, the display unit will become more important.
In the display area, there are many kinds of technologies including cathode ray tube (“CRT”), liquid crystal display (“LCD”), inorganic LED displays, and so on. LCD and inorganic LED displays may include transistors within pixel circuits. Metal-insulator-semiconductor field-effect transistors (“MISFETs”) may be susceptible to changes in threshold voltage due to charge carriers that become trapped within a gate dielectric layer. However, in the case of LCD and inorganic LED displays, the transistors are on for relatively short amounts of time, and therefore, changes in threshold voltages are not a significant problem in LCD and inorganic LED displays.
OLED technologies have great potential advantages over other display technologies, especially in larger size displays. For example, as display size increases, LCD technology has issues related to the backlight and power consumption. However, OLED material lifetime is a concern. Organic active layers, when used in radiation-emitting electronic components, have a finite lifetime. After a long time of driving a stationary image, inhomogeneity and decay of emission intensity can occur due to different driving (stress) conditions at the organic electronic level.
An anti-degradation mechanism can be used to extend the lifetime of an OLED display as the OLED material degrades. FIG. 1 includes a circuit diagram of a pixel circuit 100 (or a sub-pixel circuit) for a conventional active-matrix (“AM”) display. A select unit 102 is configured to receive signals from a select line, SL, and a data line, DL. A select signal on SL activates the select unit to pass a data signal (from DL) to a data holder unit 104 and a driving unit 106. The driving unit 106 can regulate the current flowing to the electronic component 108, which can be a radiation-emitting electronic component, and more particularly, an OLED. To reduce the effects of the use or aging of an organic active layer, an optional anti-degradation unit 110 can be used. The anti-degradation unit 110 is coupled to the data image holder 104 and the driving unit 106. The anti-degradation unit 110 can be used to reduce the charge of a capacitive electronic component within the data holder unit 104.
The anti-degradation unit does not address the threshold voltage shifts seen with MISFETs. Unlike MISFETs in LCD or inorganic LED displays, the MISFET(s) within the driving unit 106 are on for substantially longer periods of time. For example, in an LCD display, a MISFET used within the drive circuit is on for approximately 0.1% of the operational time of the display, whereas in an organic electronic device, a MISFET within the driving unit 106 can be on for substantially all the operational time of the device. With the MISFET on almost all the time, significant amounts of charge carriers can become trapped within the MISFET's gate dielectric layer and cause the threshold voltage of the transistor to drift.